The present invention relates generally to volume measurement devices, and, more particularly, to an optical volume sensor for measuring the volume of a drop of blood.
It is often necessary to quickly and inexpensively measure the volume of an object. One example of a need for volume measurement is in connection with a blood glucose monitoring system where it may be necessary to measure the volume of a drop of blood.
Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including illness such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too lowxe2x80x94a condition known as hypoglycemiaxe2x80x94a person can become nervous. shaky, and confused. That person""s judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too highxe2x80x94a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are both potentially life-threatening emergencies.
One method of monitoring a person""s blood glucose level is with a portable, hand-held blood glucose testing device. A prior art blood glucose testing device 100 is illustrated in FIG. 1. The portable nature of these devices 100 enables the users to conveniently test their blood glucose levels wherever the user may be. The glucose testing device contains a test sensor 102 to harvest the blood for analysis. The device 100 contains a switch 104 to activate the device 100 and a display 106 to display the blood glucose analysis results. In order to check the blood glucose level, a drop of blood is obtained from the fingertip using a lancing device. A prior art lancing device 120 is illustrated in FIG. 2. The lancing device 120 contains a needle lance 122 to puncture the skin. Some lancing devices implement a vacuum to facilitate the drawing of blood. Once the requisite amount of blood is produced on the fingertip, the blood is harvested using the test sensor 102. The test sensor 102, which is inserted into a testing unit 100, is brought into contact with the blood drop. The test sensor 102 draws the blood to the inside of the test unit 100 which then determines the concentration of glucose in the blood. Once the results of the test are displayed on the display 106 of the test unit 100, the test sensor 102 is discarded. Each new test requires a new test sensor 102.
One problem associated with some lancing devices is that the requisite amount of blood for accurate test results is not always obtained. Roughly thirty percent of lances to do not produce enough blood for accurate analysis. The amount of blood obtained from each lance varies between zero and ten microliters (xe2x80x9cxcexclxe2x80x9d). For an accurate result, at least two xcexcl of blood must be obtained. If less than this amount is produced, the test results may be erroneous and a test sensor is wasted. More serious an issue, however, is that the user may be relying on inaccurate results. Obviously, because of the serious nature of the medical issues involved, erroneous results are not preferred.
Another problem associated with conventional lancing devices is that there is no mechanism to let the user know whether the correct amount of blood has been obtained for accurate analysis. Typically, the test units come with instructions containing a graphical illustration of the actual size of the blood drop required for accurate testing. However, this visual comparison is subjective and often produces inconsistent results. To insure the requisite amount of blood is produced, users often overcompensate by squeezing or otherwise manipulating their fingers to produce larger than necessary drops of blood. However, this adds more time to the overall testing process and also results in an increased amount of wasted blood.
The inconsistent results produced by conventional lances has impeded the integration of the lancing device, the harvesting device, and the blood glucose analysis device into a single unit. Because the analysis may begin even though the requisite amount of blood has not been obtained, it appears problematic to combine the lancing with the actual harvesting due to the potentially inaccurate results.
According to one embodiment of the present invention, there is an optical sensor for determining the volume of an object. One application of the optical sensor is for use in a blood glucose monitoring system which integrates the lancing device. the harvesting device, and the blood glucose analysis device into a single unit. In accordance with the present invention, the optical sensor comprises a source of light and a light sensor adapted to measure an amount of light reflected off the side and off the top of a drop of blood, wherein the measured amount of the light reflected off the side and the top correlates to a height and a diameter of the blood drop. At least one optical device is adapted to direct light reflected off the side of the object to the light detector, and at least one optical device is adapted to direct light reflected off the top of the object to the light detector.
The above summary of the present invention is not intended to represent each embodiment, or every aspect, of the present invention. Additional features and benefits of the present invention will become apparent from the detailed description, figures, and claims set forth below.